CN1701043A - System and method for simultaneously heating and cooling glass to produce tempered glass - Google Patents

Abstract

A system and method for heating, shaping and tempering a glass sheet includes preheating the glass sheet to at least a first predetermined temperature. The system and method also include applying radio frequency energy to the glass sheet to heat it to at least a second predetermined temperature, and cooling at least one outer surface of the glass sheet to a third predetermined temperature to temper the glass sheet.

Description

System and method for simultaneously heating and cooling glass to produce tempered glass

Cross References to Related Applications

This application is based on US Provisional Patent Application 60/323,223, filed September 19, 2001, entitled "System for Simultaneously Heating and Cooling Glass to Produce Tempered Glass."

technical field

The present invention relates generally to tempered glass, and more particularly to a system and method for simultaneously heating and cooling glass to produce tempered glass.

Background technique

Tempered or heat-treated glasses are generally defined as pre-stressed glasses (e.g., annealed or plain glass) that have been abruptly and Rapidly quenched to be prestressed. The tempering process produces tempered glass with highly desirable induced stress conditions that result in tempered glass having additional strength, heat resistance, and impact resistance over annealed or normal glass.

The basic principle used in the tempering process is to create initial conditions of compression of the glass surface and edges. This condition is achieved by first heating the glass and then rapidly cooling the glass surface. The result of this heating and cooling is that the central layer of glass is hotter relative to the glass surface. As the central layer cools, the surface is forced to compress. Wind pressure, projectile impact, thermal stress, or other acting loads must first overcome this compression before any possibility of glass breakage can be realized.

As for the heating step, it is known that a hearth or an annealing furnace can be used to heat a glass sheet to be tempered. An annealer is a type of furnace which can be continuous roll, fixed roll or gas. For example, a gas annealer has multiple sections arranged below multiple radiant heaters. Typically, a glass sheet is placed in the lehr where the glass sheet is heated by conventional radiative, convective and conductive heating methods. The glass sheet is moved along each zone at a predetermined rate to achieve a temperature within the glass sheet forming range. The predetermined rate depends on the thermal conductivity of the glass sheet. When this temperature is reached (eg, about 1200°F), the glass sheet is formed to have the predetermined shape of the segments.

Once formed, the glass sheet is typically rapidly air quenched by passing a stream of air against it. The gas flow can be formed by arrays of fixed, reciprocating or rotating nozzles. It is important that heat is drawn evenly from both surfaces of the glass sheet (uneven heat pick-up can produce bowing or warping) and that the quench lasts long enough to prevent the glass surface from being reheated by the still hot center of the glass sheet. The quench state stabilizes when the glass sheet is lowered to a temperature of about 400°F to 600°F.

Although the lehrs described above work well, they have the disadvantage that the lehr must be sufficiently large in length to allow the glass sheet to be heated at a predetermined rate. This length requires a lot of floor space, energy consumption and cost.

A recent approach to overcome this shortcoming is to use microwave energy (with frequencies in the 2 gigahertz (GHz) to 40 gigahertz (GHz) range) to quickly and efficiently heat glass that has been preheated by traditional methods to substantially the same level or higher than glass. The temperature of the softening point of the glass plate. This approach is more fully described in Boaz, US Patent Nos. 5,782,947 and 5,827,345, the disclosures of which are incorporated herein by reference.

U.S. Patent 5,782,947 to Boaz discloses a method for heating a glass sheet comprising the steps of heating the glass sheet to a first predetermined temperature and applying microwave energy to the glass sheet to heat it to at least a second predetermined temperature such that Steps in forming a glass sheet. One advantage of the method described in US Patent 5,782,947 to Boaz is that the length of the lehr is reduced, which results in less floor space and increases glass sheet forming throughput (speed and output).

U.S. Patent 5,827,345 to Boaz discloses a method for heating, shaping and tempering a glass sheet comprising heating the glass sheet to at least a first predetermined temperature, applying microwave energy to the glass sheet to heat it to at least a first predetermined temperature. two predetermined temperatures, forming the glass sheet into a predetermined shape, and cooling at least one outer surface of the glass sheet to at least a third predetermined temperature to temper the glass sheet. One advantage of the method described in US Patent 5,827,345 to Boaz is that relatively thin glass sheets (eg, less than 0.125 inches in thickness) can be tempered. Specifically, when the center of the glass sheet is heated by microwave energy, the outer surface of the glass sheet is cooled, thereby creating the desired temperature difference or gradient between the center and outer surface of the glass sheet.

Although the methods described in U.S. Patent Nos. 5,782,947 and 5,827,345 to Boaz represent a significant advance in glass tempering technology, these methods have some disadvantages, namely the level of microwave energy disclosed (i.e., having frequencies in the 2GHz to 40GHz range) Relatively expensive to generate and maintain long production cycles. Additionally, the use of such high frequency microwave energy levels presents operational problems in conventional production equipment. Accordingly, there is a need in the art for a system and a method for rapidly, efficiently and inexpensively heating glass during the heating portion of the tempering process while maintaining the desired temperature differential between the center and outer surfaces of the glass sheet Or temperature gradient to facilitate the production of tempered glass, especially relatively thin tempered glass.

Contents of the invention

Accordingly, the present invention is a system and method for heating, shaping, and tempering a glass sheet that includes preheating the glass sheet to at least a first predetermined temperature. The systems and methods also include applying radio frequency energy to the glass sheet to heat it to at least a second predetermined temperature, and cooling at least one exterior surface of the glass sheet to at least a third predetermined temperature to temper the glass sheet.

An advantage of the present invention is that it provides a system and method for simultaneously heating and cooling glass to produce tempered glass. Another advantage of the present invention is that the systems and methods provided are particularly effective for producing relatively thin tempered glass. A further advantage of the present invention is that the system and method use radio frequency energy to rapidly, efficiently and inexpensively heat glass that has been preheated by conventional methods to a temperature substantially at or above the softening temperature of the glass. At the same time, the heated glass is cooled to maintain the desired temperature differential or gradient between the center and outer surfaces of the glass with the center having a higher temperature than the outer surfaces. Next, the treated glass sheet is quenched to produce tempered glass. The present invention also has the advantage of tempering glass of common thickness, such as 0.1875 inch thick glass, by using less compressed air to quench the heated glass.

Other features and advantages of the present invention will be better understood after reading the following description in conjunction with the accompanying drawings, making them easier to understand.

Description of drawings

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a flow diagram of a method of forming a tempered glass sheet in accordance with the present invention.

Figure 2 is a fragmentary front view of a system for forming tempered glass sheets in accordance with the present invention.

Figure 3 is a graph of the temperature differential between the center and an outer surface of a relatively thin glass sheet heated according to conventional prior art tempering techniques.

Figure 4 is a graph of the temperature differential between the center and an outer surface of a relatively thin glass sheet for simultaneous heating and cooling in accordance with the system and method of the present invention.

Figure 5 is a partial front view of another embodiment of the system for forming tempered glass sheet of Figure 2 in accordance with the present invention.

Detailed ways

Referring to Figure 1, one embodiment of a method for heating, forming and tempering a glass sheet in accordance with the present invention is shown. Although the method shown in the figures and described below is for a glass sheet, it should be understood that the method can be used for any suitable glass object.

The method includes a first step 10 of preheating the glass sheet to a temperature substantially at or above its softening temperature, which is typically in the range of about 900°F to about 950°F. This preheating can be accomplished in a number of conventional ways, including heating with infrared energy.

The method also includes a second step 20 of treating the glass sheet by heating the preheated glass sheet with radio frequency energy while simultaneously cooling at least one outer surface of the glass sheet. For example, one or more air streams are applied directly to the glass sheet to cool at least one outer surface. Preferably, the two main outer surfaces of the glass pane are cooled. Or preferably, the radio frequency energy heats the preheated glass sheet to a forming temperature in the range of about 1150°F to about 1250°F. In addition, the radio frequency energy is maintained within a frequency range of about 0.1 GHz to about less than 2.0 GHz, with a preferred frequency of 0.4 GHz.

The purpose of surface cooling of the glass sheet is to maintain the desired temperature difference or temperature gradient between the center of the glass sheet and the surface by making the center of the glass sheet have a higher temperature than the surface.

The method includes a third step 30 of quenching said treated (heated) glass sheet by a number of conventional methods to produce a tempered glass sheet. One such method is to apply one or more air streams to the treated glass sheet, preferably directed at the two major outer surfaces of the glass sheet. Or preferably, during the quenching step, the temperature of the treated glass sheet is reduced to a temperature in the range of about 400°F to about 600°F or less. After the quenching process, the tempered glass sheet is further cooled, for example, to room temperature.

Referring to FIG. 2, one embodiment of a system 100 for heating, forming and tempering a glass sheet 102 is shown in accordance with the present invention for use in conjunction with the method of the present invention. System 100 mainly includes three stations, a preheating station 104 , a heating/cooling station 106 and a quenching station 108 . Although the workstations 104, 106, and 108 are shown in close proximity, it should be understood that the workstations 104, 106, and 108 may also be separated by aisles, tunnels, ducts, tunnels, and/or other suitable structures.

The purpose of preheating station 104 (e.g., lehr, kiln, oven, or other suitable device) is to increase the temperature of glass sheet 102 substantially at or above the softening temperature of glass sheet 102, which is typically at In the range of about 900°F to about 950°F. Preferably, at least one heat source 110 (eg, an infrared heating lamp) is positioned above and/or below the glass sheet 102 as the glass sheet 102 is introduced into the preheat station 102 over a series of selectively operated rollers 112 , the rollers rotate in a desired direction to move the glass sheet 102 in a specific direction. Heat source 110 preferably heats glass sheet 102 uniformly as the glass sheet advances through heating station 104 . It should be understood that the preheated glass sheet 102a can be formed into a wide variety of shapes and configurations, such as, but not limited to, an automotive windshield (not shown).

The preheating station 104 can also be provided with a first optional door system 114a that can be opened when the glass sheet 102 is about to enter the preheating station 104 and once the glass sheet 102 has entered the preheating station 104. Selectively operated to turn on and off so as to maintain the temperature level within the preheat station 104 . In addition, the preheat station 104 may also be provided with a second optional door system 114b that is selectively operable to open when the preheated glass sheet 102a is about to enter the heating/cooling station 106, and once the preheated glass sheet 102a is about to enter the heating/cooling station 106, When the heated glass sheet has entered the heating/cooling station 106, it is closed so as to maintain the temperature level in the preheating station 104.

The purpose of the heating/cooling station 106 (e.g., an annealer, kiln, oven, or other suitable device) is to increase the temperature of the preheated glass sheet 102a to its forming temperature, which is about 1150°F to about 1250°F while cooling at least one surface of the preheated glass sheet 102a. Heating is accomplished by applying radio frequency energy to the preheated glass sheet 102a.

Preferably, at least one source of radio frequency energy, generally indicated at 116, is positioned over the preheated glass sheet 102a as it is introduced into the heating/cooling station 102 over a series of selectively operated rollers 112. Above and/or below 102a, the rollers rotate in desired directions to move the preheated glass sheet 102a in a specific direction. The RF energy source 116 includes a bus bar 118 having a plurality of electrodes 120 extending therefrom toward the preheated glass sheet 102a. A terminal portion 122 of each electrode 120 is positioned as close as possible to, but not in contact with, a major outer surface of the preheated glass sheet 102a.

As the preheated glass sheet 102a advances through the heating/cooling station 106, the RF energy source 116 uniformly heats the preheated glass sheet 102a to form a processed (heated) glass sheet 102b. The frequency of the radio frequency energy is maintained in the range of about 0.1 gigahertz (GHz) to about 2.0 gigahertz (GHz), preferably at a frequency of 0.4 gigahertz (GHz).

When the preheated glass sheet 102a is heated by the RF energy source 116 to form the treated glass sheet 102b, at least one outer surface, preferably both major outer surfaces, of the preheated glass sheet 102a/treated glass sheet 102b , are simultaneously cooled to maintain the desired temperature differential between the center of the preheated glass sheet 102a/treated glass sheet 102b and the two major outer surfaces of the preheated glass sheet 102a/treated glass sheet 102b or Temperature gradient. The center of the preheated glass sheet 102a/treated glass sheet 102b is at a higher temperature than the outer surface of the preheated glass sheet 102a/treated glass sheet 102b. Cooling is accomplished by applying at least one gas stream 129 to the preheated glass sheet 102a/treated glass sheet 102b. It should be understood that the combination of heating and cooling forms the treated glass sheet 102b.

Cooling is preferably accomplished by applying at least one stream of air or compressed air 129 to the preheated glass sheet 102a/treated glass sheet 102b. Specifically, at least one cooling system, generally indicated at 124, is disposed on the preheated glass sheet 102a/treated glass sheet 102a/treated glass sheet 102a as it advances through the heating/cooling station 106. above and/or below the glass plate 102b. The cooling system 124 includes a source 126 of compressed air 129 which is distributed through at least one nozzle, preferably a plurality of nozzles 128 . The nozzles 128 may be configured as an array of one or more stationary, reciprocating, or rotating nozzles 128 .

In another embodiment shown in Fig. 5, the electrodes 120 may be formed as tubular elements or parts 121 having at least one opening 123 to allow compressed air to flow through these tubular parts 121 to produce simultaneous cooling. Tubular members 121 are disposed between the rollers 112 above and below the glass sheet 102 to allow air to flow therethrough.

It should be appreciated that the system 100 may be used to temper relatively thin glass sheets 102 (eg, less than 0.125 inches in thickness). It should also be understood that the system 100 may be used with glass sheets of relatively normal thickness (eg, 0.375 inches in thickness and height) for tempering using less quench compressed air. It should also be further understood that one or more temperature measuring devices (not shown) may be used to measure the temperature of the preheated glass sheet 102a/processed glass sheet 102b. It should be further understood that the processed glass sheet 102b can be formed into a variety of shapes and configurations, such as, but not limited to, automotive windshields (not shown).

The heating/cooling station 106 may also be provided with an optional door system 130 which is selectively operable to open when the processed glass sheet 102b is to be pushed out of the heating/cooling station 106 and once processed When the last glass sheet 102b has entered the quench station 108, it is closed, thereby maintaining the temperature level within the heating/cooling station 106.

The purpose of the quench station 108 is to abruptly and rapidly quench the treated glass sheet 102b to form a tempered glass sheet 102c. Preferably, the temperature of the treated glass sheet 102b is reduced to a temperature in the range of about 400°F to about 600°F or less during the quenching process so as to form the tempered glass sheet 102c. After the quenching process, the tempered glass sheet 102c may be further cooled, for example, to room temperature.

Quenching is preferably accomplished by applying at least one gas stream 132 to the treated glass sheet. In particular, at least one cooling system, generally indicated at 134, is disposed above the treated glass sheet 102b/tempered glass sheet 102c as the processed glass sheet 102b/tempered glass sheet 102c advances through the quench station 108 and/or below. Preferably, the cooling system 134 uniformly cools the processed glass sheet 102b as the processed glass sheet 102b advances through the quench station 108 to form the tempered glass sheet 102c.

The cooling system 134 preferably includes at least one source 136 of compressed air 132 that is distributed through at least one nozzle 138, preferably through a plurality of nozzles. The nozzles 138 may be configured as one or more arrays of fixed, reciprocating or rotating nozzles.

The quenching station 108 may also be provided with an optional door system 140 which is selectively operable to open when the tempered glass 102c is about to be pushed out of the quenching station 108 and once the tempered glass sheet 102c has been removed from the quenching station 108. It is closed when ejected to atmosphere, thereby maintaining the temperature level within the quench station 108 .

Referring to Figures 3 and 4, the relationship between the central temperature "a" of a relatively thin glass sheet 102 and the temperature "b" of one of its outer surfaces is shown in a conventional tempering system and method and in the tempering system and method of the present invention, respectively. The graph contrast of the temperature difference (δt) between them. Figure 3 shows that a conventionally quenched relatively thin glass sheet 102 heated in a conventional manner produces a relatively small temperature difference (δt) between a central temperature "a" of the glass sheet and an outer surface temperature "b". That is, there will not be a very large temperature difference between the center and the outer surface of the glass sheet 102 . As the treated glass sheet 102b is quenched, induced stresses will not be likely to develop within the glass sheet 102 without a significant temperature differential (δt), which is therefore very undesirable for tempering a relatively thin glass sheet 102 .

In contrast, FIG. 4 shows that a conventionally quenched relatively thin glass sheet 102 heated in accordance with the present invention produces a temperature difference between a glass sheet center temperature "a" and an outer surface temperature "b" compared to conventional tempering techniques ( δt) greater temperature difference (δt). That is, a greater temperature differential is created between the center and outer surfaces of the glass sheet 102 than would result from conventional tempering techniques. This temperature differential is ideal for tempering a relatively thin glass sheet 102 as the treated glass sheet 102b is quenched since a significant temperature differential (δt) will allow induced stresses to develop within the glass sheet 102 .

Accordingly, the present invention employs radio frequency energy in the heating or treating portion of the tempering process to heat preheated glass sheets quickly, efficiently and inexpensively. At the same time, one or more air streams are preferably used during the tempering process to maintain the desired temperature difference or gradient between the center of the glass sheet and at least one of its outer surfaces. Next, the treated glass sheet is quenched to produce tempered glass.

The present invention has been described by way of example. It is understood that the words used are merely illustrative and not restrictive.

Many modifications and variations of the invention are possible in light of the above description. Therefore, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

Claims (23)

1. A method for heating, forming and tempering a glass plate, comprising the steps of: preheating the glass sheet to at least a first predetermined temperature; applying radio frequency energy to the glass sheet to heat the glass sheet to at least a second predetermined temperature; Cooling at least one outer surface of the glass sheet to at least a third predetermined temperature tempers the glass sheet. 2. The method of claim 1, wherein the radio frequency energy has a frequency in the range of about 0.1 GHz to about 2.0 GHz. 3. The method of claim 1, wherein the radio frequency energy has a frequency of approximately 0.4 GHz. 4. The method of claim 1, wherein the cooling step includes directing at least one air stream onto at least one outer surface of the glass sheet. 5. The method of claim 1 including the step of quenching the glass sheet to produce a tempered glass sheet. 6. The method of claim 5, wherein said quenching step includes applying at least one gas flow to at least one outer surface of the treated glass sheet. 7. The method of claim 5 wherein said quenching step reduces the temperature of the treated glass sheet to a temperature in the range of about 400°F to about 600°F. 8. The method of claim 1, wherein the heating and cooling steps include providing at least one hollow electrode, from which radio frequency energy is applied to the glass sheet, and through the electrode to at least one outer surface of the glass sheet At least one draft. 9. The method of claim 1 wherein said first predetermined temperature is a temperature in the range of about 900°F to about 950°F. 10. The method of claim 1 wherein said second predetermined temperature is a temperature in the range of about 1150°F to about 1250°F. 11. The method of claim 1 wherein said step of preheating the glass sheet to at least a first predetermined temperature comprises heating with infrared energy or convective energy. 12. A system for heating, forming and tempering glass sheets comprising: a preheating station having at least one heat source disposed above and/or below the glass sheet and adapted to raise the temperature of the glass sheet to a temperature substantially equal to or above the softening point of the glass sheet; A heating/cooling station having at least one source of radio frequency energy positioned above and/or below the glass sheet and adapted to raise the temperature of the preheated glass sheet to substantially equal or greater than the preheated The temperature at which the glass sheet is formed; A cooling station for raising the temperature of the center of the glass sheet above an outer surface temperature to maintain the desired temperature differential between the center of the glass sheet and the outer surface to form tempered glass by a combination of heating and cooling plate. 13. The system of claim 12, wherein the at least one radio frequency energy source emits energy having a frequency in the range of about 0.1 GHz to about 2.0 GHz. 14. The system of claim 12, wherein said at least one source of radio frequency energy emits energy having a frequency of approximately 0.4 GHz. 15. The system of claim 12, wherein said at least one source of radio frequency energy comprises a bus bar with a plurality of electrodes extending therefrom toward the glass sheet, each of said electrodes having a terminal A portion, which is arranged as close as possible to one outer surface of the glass sheet but in a non-contacting relationship, and is adapted to heat the glass sheet. 16. The system of claim 12, wherein said at least one source of radio frequency energy comprises at least one hollow electrode to enable application of radio frequency energy to the glass sheet, and is connected to a source of compressed air to pass through said at least one A hollow electrode enables compressed air to be applied to the glass plate. 17. The system of claim 12, wherein said preheat station comprises a series of selectively operable rollers that rotate in a desired direction to introduce the glass sheet into said preheat station, and A glass sheet is moved through the preheating station in a specific direction. 18. The system of claim 12, wherein said heating station comprises a series of selectively operable rollers that rotate in a desired direction to introduce the glass sheet into said heating/cooling station, And moving the glass sheet through the heating/cooling station in a specific direction. 19. The system of claim 12, including a quench station adapted to rapidly quench the glass sheet to form a tempered glass sheet. 20. The system of claim 19, wherein said quench station comprises a series of selectively operable rollers that rotate in a desired direction to introduce the glass sheet into said quench station and along a specific direction to move the glass sheet through the quench station. 21. The system of claim 12, wherein the cooling station includes at least one cooling system disposed above and/or below the preheated glass sheet so that the glass sheet advances through the heating station Apply compressed air while in position. 22. A system for heating, forming and tempering glass sheets comprising: a preheating station having at least one heating source disposed above and/or below the glass sheet and adapted to raise the temperature of the glass sheet to a temperature substantially equal to or above the softening point of the glass sheet; A heating/cooling station having at least one source of radio frequency energy positioned above and/or below the glass sheet adapted to raise the temperature of the preheated glass sheet to substantially equal or greater than the temperature of the preheated glass sheet The temperature at which the sheet is formed and the temperature at the center of the glass sheet is higher than that of an outer surface to maintain the desired temperature differential between the center of the glass sheet and the outer surface to form tempered glass by a combination of heating and cooling plate. 23. The system of claim 22, wherein said at least one source of radio frequency energy comprises at least one hollow electrode to enable application of radio frequency energy to the glass sheet, and is connected to a source of compressed air to pass through said at least one A hollow electrode enables compressed air to be applied to the glass plate.

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